This invention relates to a refrigerant compressor adapted primarily for use in air conditioning systems, and more particularly to a vane compressor having an improved device for applying back pressure to the vanes.
Vane compressors are widely employed as refrigerant compressors in air conditioning systems for automotive vehicles, in general, by virtue of their simple construction and adaptability to operation at high rotational speeds.
As one of vane compressors of this kind, there has conventionally been used a type which includes a pump housing formed by a cam ring and front and rear side blocks secured to opposite ends of the cam ring and accommodating a rotor and vanes, a casing accommodating the pump housing and defining a discharge pressure chamber in cooperation therewith, and a drive shaft extending through the front and rear side blocks and the casing and carrying the rotor secured thereon, and a pair of radial plane bearings formed integrally with the front and side blocks and supporting the drive shaft.
In this type conventional vane compressor, the front and side blocks are each formed therein with a radially extending lubricating oil passage which opens at one end in the discharge pressure chamber and at the other end in the sliding peripheral surface of the corresponding radial plane bearing.
During operation, lubricating oil stored on the bottom of the discharge pressure chamber is forcedly guided through the lubricating oil passages and then through fine clearances between the drive shaft and the radial plane bearings, into a drive shaft-sealing chamber and an oil chamber formed at opposite sides of the radial plane bearings remote from the rotor, and thereafter it is supplied into a back pressure chamber formed within the rotor to apply its own pressure to the vanes as back pressure, while lubricating various sliding portions along its route.
In order to apply a predetermined proper back pressure to the vanes, the clearances between the radial plane bearings and the drive shaft are set at such a value as to produce a value of flow resistance acting upon the lubricating oil passing therein such that the lubricating oil has its pressure reduced from an original high discharge pressure level (e.g. about 15 kg/cm.sup.2) to a back pressure level (e.g. about 8.5 kg/cm.sup.2) which is intermediate between the discharge pressure level and a suction pressure level (e.g. about 2 kg/cm.sup.2). On the other hand, it is a requisite that this clearance value should not be too large enough to spoil the proper bearing function of the radial plane bearings, that is, the function of supporting the drive shaft while allowing free and smooth rotation of same. Therefore, in the above conventional vane compressors, the above clearance value is set at approximately 0.005 mm, for instance, so as to satisfy both the pressure reducing function of the bearings and the bearing function of same.
However, when the compressor is starting, or when thermal load on the air conditioning system is small even during normal steady operation of the compressor, for instance, in a season such as spring and fall, the discharge pressure of the compressor is so small that the difference between the discharge pressure and the suction pressure is not so large as to apply sufficient back pressure to the vanes, because the pressure of lubricating oil supplied to the back pressure chamber through the aforementioned clearances is too small. As a consequence, the vanes cannot maintain its close contact with the camming inner peripheral surface of the cam ring while it is sliding thereon, causing chattering, which results in a reduction in the compression efficiency as well as damage to the compressor parts. To avoid such disadvantage, one would hit upon an idea of providing oil passages for directly guiding lubricating oil from the lubricating oil passages to the back pressure chamber while bypassing the aforementioned clearances. However, to produce required large flow resistance in such oil passages, the diameter of them has to be set at a very small value such that boring of them is practically impossible, whereas if the diameter is set at a larger value so as to enable boring, the resultant flow resistance is too small such that high pressure nearly equal to the discharge pressure prevails in the back pressure chamber, which causes wear of the vanes as well as energy loss.